Volume dispensers based on feed screws and used in stalls or on feed trucks are often used as being somewhat cheaper and simplier alternatives compared with weight dispensers. Usually horizontal or upward directed feed conduits with constantly open outlets are used. Due to the pulsating delivery obtained from such devices, a certain inaccuracy in the portioning, as determined by the occasional stop position of the screw, must be accepted. A further disadvantage with open feed conduit at animal feeding is that the animals by means of impacts and bangings on the device or the stall equipment with a certain success can get feed stuff out from the device even between feeding periods, thereby further reducing the portioning accuracy and damaging the equipment.
To solve the above mentioned problems, it has been proposed to provide portioning devices with various closing devices. According to one proposal, which relates to a dispenser with horizontal feed screw, in order to prevent further feed stuff delivery after the screw has stopped, the end of the feed tube has been provided with a cylindrical shutter device that through control means can be turned concentrically around the feed tube. Another proposal provides a horizontal screw dispenser, the outlet end of which is simply provided with a shutter being operable in the vertical direction. Beside the fact that these shutter devices fixed to the feed tube require comparatively awkward control equipment to be automatically synchronized with the dispenser screw, the range of uncertainty depending on the said pulsating delivery can only be partially reduced in this way.
Even screw based volume dispensers having vertical or downwards sloping delivery tube have been suggested for the purpose of avoiding said pulsating delivery. As closing means in this context, it has been suggested to use gates pivotally or slidably fixed at the delivery tube. In addition to the problem already mentioned of synchronizing the closing device to the screw, this solution was generally refused since the desired portioning accuracy was never obtained due to reasons such as accumulation of stuff on shutter parts below the screw, stuff that sticks between the shutter and the feed conduit wall at the closing operation etc.
Vertical feed screw based dispensers are also known, which are provided with axial closing devices that are not fixed to the feed but to the rotating screw. One such closing device is formed by a circular disc of elastic material fixed at the screw shaft. The operation principle of the device is that the disc is bent downwards by the feed pressure formed at rotating the screw so that an annular opening is formed at the tube wall. The same principle has been proposed in another form according to which, however, the main purpose of the flexible disc is to form a lock to prevent pressure equalization between the room connected to the inlet of the screw conveyor and the room connected to the outlet of the screw conveyor. In addition to the fact that the delivery openings formed according to this principle are generally too small for the majority of the volume portioning applications and further do not permit the desired accuracy, it is based on the phenomenon that by all means is to be avoided in context with foodstuff portioning, that is compression of the material. Compression of feed concentrate and many other materials is known to create variations in the bulk density depending on where the material is positioned along the screw conveyor and to increase the always undesired tendency of material separation into different particle fractions.
The present invention has the object to achieve a screw based volume dispenser having a feed conduit provided with closing means, that is safe in operation and improves the portioning accuracy. A further object of the invention is a dispenser that is constructed to permit volume portioning through a vertical or downwards directed screw feed conduit. Still a further object is to provide a screw based volume dispenser with closing means that in a simple way can be coupled to the screw for automatic opening of the outlet conduit when the screw is started and automatic closing of said conduit when the screw stops.